1. Field of the Invention
This invention relates to new stable bacteriochlorins generally having long wave length absorptions between 700 and 800 nm. Such compounds have utility as photsensitizers for photodynamic therapy (PDT).
2. History of the Prior Art
PDT has emerged as one of the promising strategies in cancer treatment. In this therapy, patients are given intravenous injections of a porphyrin-based drug that accumulates in cancer cells in generally higher concentrations than in surrounding tissue. The photosensitizing agent is then activated by a visible or near IR light to cancer sites through fiber optics which following energy transfer to molecular oxygen produces the singlet oxygen, the putative cytotoxic agent. PDT is thus a novel and potentially important form of cancer therapy. At presents efforts are underway in various laboratories to prepare photosensitizers exhibiting long wavelength absorption near 700–800 nm, which could enable to treat large tumors due to deeper light penetration in tissues at that wavelength. Therefore, during last ten years a variety of naturally occurring bacteriochlorins (porphyrin systems in which two pyrrole rings diagonal to each other are reduced) have been synthesized and evaluated for PDT efficacy. Unfortunately, most of the naturally occurring bacteriuochlorins (e.g. bacteriochlorophyll-a) are not stable in vivo and slowly convert into chlorin systems.